PLC and Operator Interface Advantages Stack Up for a Large Container Automatic Stacking

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PLC and Operator Interface Advantages Stack Up for a Large Container Automatic Stacking Crane Project
PLC and Operator Interface Advantages Stack Up for a Large Container Automatic Stacking Crane Project

The Port of Virginia operates two inland and four coastal marine ports. As shipping demand continued to grow, in 2017 the Port embarked upon a project to expand two of these sites, at the Norfolk International Terminal (NIT) and the Virginia International Gateway (VIG) facilities. A major part of this expansion included the supply and integration of 86 automated-stacking cranes (ASCs), which was the largest single ASC project ever initiated by a port (Figure 1).

Figure 1: The Port of Virginia added 86 automated-stacking cranes using PLC-based automation integrated by TMEIC under Konecranes’ turn-key ASC system delivery to VIG. Photo courtesy of Port of Virginia.

To carry out a project of this scale and complexity, the TMEIC Corporation (Toshiba Mitsubishi-Electric Industrial Systems Corporation) in Roanoke VA was retained to provide an industrial drive and automation solution for the Konecranes ASC system. TMEIC already had a long and successful history with the Port, having been involved with the original VIG ASC implementation with Konecranes a decade earlier.
 
The new expansion would rely in part on updated programmable logic controller (PLC) and human-machine interface (HMI) automation. Integration would provide advanced remote-control capabilities so operators could work from a centralized control room—instead of a crane cab—using video, advanced sensor technology, and HMI displays. The PLCs directly controlling this massive crane equipment with exquisite accuracy needed to provide robust operation, extensive connectivity, and scalable architectures.
 

Heavy lifting

Cranes designed to transfer standard shipping containers among ships, storage yard stacks, rail cars, and truck trailers have been a fundamental part of modern high-efficiency logistics and shipping for many years. Although to some the equipment may seem large, lumbering, and decidedly old-school, there is a great amount of detailed coordination and sophisticated technology operating behind the scenes (Figure 2).

Figure 2: Large cranes rely on modern PLCs, advanced sensors, and responsive integration with motor drives for positioning with an accuracy of better than 50mm. Photo courtesy of TMEIC.

These rail-mounted gantry (RMG) cranes move in 3 axes. The gantry is the entire assembly which rolls forward and backward on wheels along the entire length of container stacks, often on rails or tracks, while the trolley is the upper part of the gantry and it can move left and right along the width of the crane across the stacks. The hoist uses cables to support and position a gripping mechanism—also known as a spreader—to lift and lower containers in the vertical axis (Figure 3).

Figure 3: The gantry, trolley, and hoist provide three degrees of motion, and the automation system must act to dampen undesired cargo movement. Photo courtesy of TMEIC.

Payloads can be unevenly loaded, and this weight differential makes them more difficult to handle and place. Because the cargo containers hang down from cables and the whole assembly is movable, there are mechanical reeving features to dampen motion, and the drive systems must also incorporate active dampening. A standard cargo container is 40 feet long and can weigh up to 40 tons, yet it needs to be captured successfully, and then landed with an accuracy of 50mm.
 
Many years ago, cranes were fully controlled by operators who sat in cabs high on the gantry so they could have a clear view of the work. Once video and PLC technology improved sufficiently, it was possible to locate operators in a control room (Figure 4).

Figure 4: Integrated video and control consoles enable operators to monitor and control cranes. Photo courtesy of TMEIC.

This paradigm of remote ASC operation began internationally in the late 1980’s. In 2007, TMEIC automated the first North American ASC at VIG as part of Konecranes’ turn-key ASC system delivery. TMEIC has integrated and automated over 600 ASCs worldwide, establishing them as a leader in the field.
 
Remote operation makes cranes lighter and improves safety. It also lets a few expert operators control whichever crane is ready for operation, instead of having operators move from crane to crane, which in some cases requires traversing hundreds of yards.
 
The latest evolution is modern ASCs, which incorporate advanced computing, sensors, and networking to automate most aspects of operation. Operators closely monitor automatic operation and may become involved to perform the initial container capture, complete the final release (especially if the designation is a trailer chassis), or take action if there is an issue. Otherwise, the container will travel from pick-up to drop-off location automatically in the optimal manner (Figure 5).

Figure 5: Modern HMIs provide crane operators with detailed feedback regarding the status of crane and cargo handling operations. Photo courtesy of TMEIC.

Integration of advanced sensors with the automation platform makes this possible. The main instrument is a LIDAR-based laser distance sensor, and the gantry and trolly are instrumented with RFID pucks so their locations can be determined within a range of 15mm and 5mm respectively.
 
From a port logistics standpoint, a software-based overall management system called the terminal operator system (TOS) coordinates and schedules all movements. Loading and unloading vessels takes priority. When the ASCs are not occupied with loading and unloading operations, the TOS may direct a buried container to be made accessible, or perform background tasks like handling a queue of containers to be moved around the yard to groom the stacks and optimize upcoming operations. One last detail is that ASCs operate in pairs with overlapping paths, so special deadlock logic must be implemented to ensure neither ASC interferes with the other.
 

Technical and logistical challenges

To successfully achieve the necessary functionality and address all technical requirements, the right automation platform was required. Many capabilities had improved between 2007 and 2017, but after reviewing the TMEIC team determined PLC-based technology was still the right choice. New demands included networking and communication for integrating intelligent sensors, communicating with the supervisory TOS, and scaling up with so many ASCs.
 
For instance, the improved LIDAR systems use proprietary main control units in order to resolve distances with high accuracy. The PLCs would need to rapidly interrogate these intelligent distance sensors via the control units to obtain responsive positioning information. For all new PLC communications, the team wanted to take full advantage of modern OPC UA and Ethernet Global Data (EGD) communications. The latter would ensure compatibility of the 86 new ASCs with the 30 existing units to the greatest extent possible. In fact, at some point it would be likely that new automation devices and sensors might be retrofitted to existing equipment.
 
AC variable speed drives (VFDs) used in the motor drive panels had also gained intelligence over this time period, and the PLCs would need an even greater amount of communication capabilities to take advantage of these advances for remotely commanding parameters like speeds and ramp rates, and deeply interrogating the available performance and diagnostic data.
 
TMEIC scope included designing control panels, yard I/O panels, motor drive panels and all integration from their Virginia-based North American headquarters. On top of these technical tasks, there were the logistics of coordinating activities among many international team members from TMEIC’s Virginia-based location:

  • Konecranes is a Finland-based company
  • The cranes are physically fabricated and assembled in Poland
  • Pre-assembly would include a degree of electrical and functional testing in Poland
  • After pre-assembly and testing, the mechanical and electrical designs needed to support disassembly and transportation over the ocean via BigLift Shipping
  • Each remote operator station was built in Italy and would be shipped direct to VIG and NIT, except for a handful shipped to Poland for integrated testing, and yard I/O panels were assembled and shipped from various locations
  • TMEIC-supplied motor drive panels were fabricated in Japan and shipped to Poland for integration
  • Motors and other advanced sensors were procured from various sources worldwide

While the crane manufacturer designed and built the mechanical equipment, TMEIC provided all electrical and automation equipment by applying their specific knowledge of drives and automation developed in this sector over many years. With the requirements clearly defined, the TMEIC automation team proceeded with detailed design.
 

PLC integration advantages

The first generation of ASCs at VIG predominantly used PACSystems RX3i PLCs, which still serve reliably today. For best interoperability, the natural choice moving forward was to select the newest generation of Emerson’s robust PACSystems RX3i PLCs. Emerson’s strong focus on providing end users with a simple and easy upgrade path for both control hardware and software, along with its commitment to expanding open communications and advanced…

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